Although relatively new on the scene, aspirating smoke detection systems have quickly found a niche in critical asset protection and challenging environments. Now with the completion of a new European standard, they really can be said to have come of age. Peter Massingberd-Mundy explains.
Aspirating smoke detection systems need little introduction these days; they are deployed extensively and account for more than 7% of the detection market in Europe(1). Aside from this commercial recognition, the technology is the subject of a new European product standard – EN54-20 ‘Fire detection and fire alarm systems – Part 20: aspirating smoke detectors’ – which within the conservative fire industry is a strong testament to its pedigree.
This new standard, in conjunction with the latest codes of practice, will help to ensure that the reliable performance and good reputation of these systems is not eroded by unapproved and inappropriate products. In the words of Richard Philips, technical director (electronics) with the Loss Prevention Certification Board (LPCB), “ASD has come of age!”
This article provides some insight into the details of EN54-20. It highlights the key changes from the test requirements defined in CEA4022 and, more importantly, describes how these changes, supported by the recently updated BFPSA code of practice for aspirating smoke detection systems, will be of benefit to installers and users of the technology.
The fire industry is highly regulated, with many product and application standards. The importance of product standards must not be underestimated, as they are the foundation of prescriptive-based application rules or codes (such as BS5839 Part 1) and are equally important to the emerging performance based design approaches.
However, it takes many years to develop and agree product standards and they do not generally support innovative technology. Fortunately, the wide adoption of an innovative product is possible when backed by appropriate testing and approval by the recognised independent authority. This is exactly what happened over 10 years ago when aspirating smoke detection was an innovative technology. It was shown by the hot wire performance test to outperform conventional detection methods in telecoms and computer environments with high airflows. Together with VdS and others within the CEA (Comite Europeen des Assurances), LPCB developed a product standard for ASD systems based on the requirement that they must, as a minimum, perform as well as conventional point detectors. The key requirements were to:
– successfully detect the four standard test fires used to test point detectors;
– pass all environment tests used in the testing of point detectors; and
– ensure that failure of critical components is monitored – for example, aspirator failure, blockage of the holes or failure of the sampling pipes must raise a fault.
From this work a document, GEI 1-048, was published, which was used to approve the first aspirating systems. This subsequently became CEA 4022, which was endorsed (nearly five years later) by EFSAC (European Fire and Security Advisory Council).
In 1998, recognising the existing and potential growth in these systems, CEN TC72 was mandated to prepare a European standard for the type approval of aspirating systems. After much deliberation, including the development of six new fire tests, Working Group 16 completed the first draft, which was circulated for comment in October 2003. The final version incorporating all the feedback was completed in July 2005. It received a positive vote from CEN TC72 in April this year, and is due to be published by CEN imminently.
What’s new in EN54-20?
The key changes in EN54-20 concern fire testing and airflow monitoring. For airflow monitoring (the method by which the integrity of airflow through the sampling pipe network is monitored), the requirement has become more stringent. Previously, the CEA document required that a change in airflow of +/-50% be detected within a given time and indicated as an airflow fault. EN 54-20 requires the criteria to be met upon a change of +/-20%. This is a clear step change in the requirement which could present some engineering challenges for manufacturers, but should result in greater system reliability.
EN54-20 also requires that flow normalisation (whereby the ‘normal’ flow is memorised and used as the reference for the detection of subsequent deviations) can only be done as a “voluntary action under level 3 access”. Furthermore, correct functioning of the airflow monitoring is now checked during the hot, cold and operational damp heat tests – this was not the case in the original standard.
For fire testing, EN 54-20 has introduced a fire sensitivity classification system incorporating classes A, B and C. The fire tests are based upon the ‘TF’ series of test fires, previously seen in EN 54-7 for optical point smoke detectors and earlier aspirating detection standards. The Class C test fires are the same as those for EN54-7 and serve to demonstrate ‘normal’ sensitivities. Classes A and B – high sensitivity and enhanced sensitivity respectively – employ new fires with less initial fuel. They also use a smoke ‘stirring’ mechanism to mix the smoke and air in the test room, effectively producing a repeatable diluted smoke mixture.
In addition to this crucial introduction of a classification system, EN54-20 has updated the pass criteria for the fire tests. In the former standard the detector could signal an alarm after the defined End of Test (EoT), recognising that there is an inherent transport time delay in aspirating systems. Essentially, it was acknowledged that as long as the smoke had entered the sample point before the fire finished then an alarm was inevitable – albeit some time later. This meant that an approved system could respond up to 120 seconds after a conventional point detector. Some manufacturers exploited this concession to the full, while others have conscientiously shown during approval testing that their systems are able to signal an alarm before the defined EoT, without making any allowances for transport time. In recognition of this dichotomy, EN54-20 still permits that alarms can be signalled after the EoT, but only up to a maximum of 60 seconds. Actual transport times may exceed 60 seconds during the test – in fact they are not limited.
The first and most important benefit to installers and their customers is that EN54-20 is a mandated standard under the Construction Product Directive (CPD). As such it incorporates an Annex Z, which outlines the requirements and timings for CE marking of the product. Essentially, after 2009, all ASD systems in Europe will be required to be independently tested to EN54-20, thus shoring up the product standard which is the foundation for reliable smoke detection in the field.
Benefits of the new standard
In terms of application, the classification system introduced by EN54-20 will enable specifiers and installers to clearly define the capability of the system they wish to use. Class A is for high sensitivity detection, for early warning of smoke conditions in a high-flow environment; Class B is for enhanced sensitivity, for reliable detection of smoke in an open area with high ceilings where smoke dilution is a challenge; and Class C is for a normal sensitivity detector installed in an area where maintenance access is limited. The BFPSA code of practice provides further excellent guidance on how this new classification system can be used effectively during the specification of a system. It describes a simple technique where any system can be described in terms of its EN54-20 sensitivity class, the sampling technique (e.g. primary or secondary), the design requirement (whether based on prescriptive standards or performance-based design), and the principal drivers for using aspirating detection in that particular application.
The tighter airflow requirements of EN54-20 will, most likely, improve the airflow monitoring technology used in aspirating systems. Less capable systems will struggle to meet the new requirements – perhaps due to the new +/-20% limit; perhaps because the monitoring is not sufficiently temperature-compensated; or perhaps because they normalise themselves whenever they are turned on.
For installers, improved flow monitoring will reduce the number of nuisance faults, while for end users, the improvements will provide further confidence that the system they are using is fit for purpose. It is worth noting that some systems already meet the +/-20% limit, as it has been a requirement of the Austrian standard for some years.
According to an I&I Proplan survey(1), while aspirating smoke detection accounts for about 7% of the total spend on fire detectors in Europe, the UK dominates with a reported spend of 13%. France – at 7% – uses the next highest proportion while Germany, Italy, Spain, Netherlands and Belgium all use about 5%. What accounts for this difference?
One of the main reasons the UK market is more comfortable with the technology is because it has traditionally used higher specification early warning products, such as VESDA. In the rest of Europe the tendency has been to use a higher proportion of low specification systems, often referred to as point in a box (PIAB) technology. Of course, it can be argued that PIAB technology has a lower cost than the higher sensitivity systems, but this is not sufficient to account for the marked difference in the usage figures between the UK and the rest of Europe.
Another reason for the difference is that the UK is generally less conservative and more tolerant of technology that may not comply to the letter of the codes of practice. Indeed, UK codes of practice, such as BS5839-1 (section 7), clearly state that they provide recommendations not requirements, and are based on recognised good practice. By contrast, the tendency in other parts of Europe is to adhere to the recommendations as if they are rules – unless there are exceptional circumstances. As such, the benefits of early warning systems with multistage alarms are not exploited as widely on the continent as they are in the UK. The new classification system in EN54-20 will help to clarify the different capabilities of the systems available and will, over time, be adopted into the various application codes across Europe. As such, it can be anticipated that the proportion of high specification systems is likely to increase. Nevertheless, it is important that practitioners understand that the EN54-20 classification system is not perfect, and should not be used as a single comparator when considering which system to use.
For a start, it should certainly not be used as an indicator of quality. The certification to a class only gives an indication of detector sensitivity, and does not illustrate whether a product provides any other valuable features. Astute buyers should satisfy themselves that the solution provides other important features such as: the number of alarm thresholds; flexibility in configuration; ease of use, maintenance and fault finding; and perhaps, most importantly, the stability of the detection method and its robustness in a wide range of environments.
Even regarding sensitivity, the classification system should be used with caution because, while a Class C normal sensitivity system with several holes would not be expected to detect Class A or Class B test fires, it can most likely detect Class B fires when configured with only a couple of sampling holes. By contrast, a fully capable Class A high sensitivity detector might be able to detect Class B fires, even when configured with a large number of sampling holes. Both may be approved as Class B detectors, but one is clearly more capable and is able to support more holes and greater dilution than the other. Unfortunately, in spite of proposals that it should, the classification system does not extend to providing any indication of the dilution factor. As such, it will be possible for relatively low sensitivity systems to be marketed as Class B (or even Class A) detectors – without any indication of the number of holes supported. The only requirement in EN54-20 is that “the manufacturer shall … provide the necessary means to determine the classification of any used configuration”. Such “means” may only be available in the supporting technical documentation and so would be relatively inaccessible until after purchase. So specifiers, installers and users of aspirating systems should ensure that they have full information on the configuration and class of any particular system, and should be cautious of systems which do not clearly state how the class of a particular configuration can be determined.
Summary
EN54-20 is a new product standard for the fire detection market and, as a mandated standard under the Construction Products Directive (CPD), will become the foundation for reliable aspirating smoke detection in the future. It was developed from existing standards and incorporates a number of important changes – not least the introduction of a classification system to help practitioners define the installed sensitivity of systems. Unfortunately, the new classification framework does not provide a clear indication of the maximum number of holes supported, so it is cannot be used to compare the capability of one detector versus another. However, as the installation codes of practice across Europe adopt the new classifications (as has already been done with the BFPSA code of practice) there will be wider adoption of the technology in an increasing range of applications – from applications requiring Class C systems where aspirating detection provides important practical advantages over other techniques, through Class B systems where the enhanced sensitivity can overcome environmental challenges to detection of smoke, to Class A systems which can provide the earliest possible warning of a fire – allowing the maximum possible time to investigate, respond and mitigate any threat to life or property.
Peter Massingberd-Mundy is technology and expert practises manager at Vision Fire and Security and sits on CEN TC72 working group 16 which developed the new EN54-20 standard.
Reference
1. I&I Proplan study European fire market 2003 – 2008 www.iand.ltd.uk
